The Bulgeless Seyfert/Liner Galaxy Ngc 3367: Disk, Bar, Lopsidedness, and Environment∗

THE BULGELESS SEYFERT/LINER GALAXY NGC 3367: DISK, BAR, LOPSIDEDNESS, AND ENVIRONMENT∗

H. M. Hernandez-Toledo´ 1, M. Cano-D´ıaz1,2, O. Valenzuela1, I. Puerari3, J. A Garc´ıa-Barreto1, E. Moreno-D´ıaz1, and H. Bravo-Alfaro4 1 Instituto de Astronom´ıa, Universidad Nacional Autonoma´ de Mexico,´ Apartado Postal 70-264, Mexico´ D. F., 04510, Mexico; [email protected] 2 INAF-Osservatorio Astronomico di Roma, via di Frascati 33, 00040, Monte Porzio Catone, Italy 3 Instituto Nacional de Astrof´ısica, Optica´ y Electronica,´ Calle Luis Enrique Erro 1, 72840, Sta. Maria Tonantzintla, Puebla, Mexico 4 Departamento de Astronoma, Universidad de Guanajuato, Apdo. Postal 144, Guanajuato 36000, Mexico Received 2008 October 15; accepted 2011 March 29; published 2011 October 31

ABSTRACT NGC 3367 is a nearby isolated active galaxy that shows a radio jet, a strong bar, and evidence of lopsidedness. We present a quantitative analysis of the stellar and gaseous structure of the galaxy disk and search for evidence of recent interaction. Our study is based on new UBVRI Hα and JHK images and on archive Hα Fabry–Perot and H i Very Large Array data. From a coupled one-dimensional/two-dimensional GALFIT bulge/bar/disk decomposition a(B/D ∼ 0.07–0.1) exponential pseudobulge is inferred in all the observed bands. A near-infrared (NIR) estimate max = of the bar strength QT (R) 0.44 places NGC 3367 bar among the strongest ones. The asymmetry properties were studied using (1) the optical and NIR concentration–asymmetry–clumpiness indices, (2) the stellar (NIR) and gaseous (Hα,Hi) A1 Fourier mode amplitudes, and (3) the H i-integrated profile and H i mean intensity distribution. While the average stellar component shows asymmetry values close to the average found in the local universe for isolated galaxies, the young stellar component and gas values are largely decoupled showing significantly larger A1 mode amplitudes suggesting that the gas has been recently perturbed and placing NGC 3367 in a global starburst phase. NGC 3367 is devoid of H i gas in the central regions where a significant amount of molecular CO gas exists −2 instead. Our search for (1) faint stellar structures in the outer regions (up to μR ∼ 26 mag arcsec ), (2) (Hα) star-forming satellite galaxies, and (3) regions with different colors (stellar populations) along the disk all failed. Such an absence is interpreted by using results from recent numerical simulations to constrain either a possible tidal event with an LMC like galaxy to some dynamical times in the past or a very low mass but perhaps gas rich recent encounter. We conclude that a cold flow accretion mode (gas and small/dark galaxies) may be responsible for the nuclear activity and peculiar (young stars and gas) morphology regardless of the highly isolated environment. Black hole growth in bulgeless galaxies may be triggered by smooth mass accretion. Key words: galaxies: active – galaxies: general – galaxies: individual (NGC 3367) – galaxies: interactions – galaxies: structure – galaxies: photometry Online-only material: color figures

1. INTRODUCTION Radio observations in NGC 3367 reveal a bipolar synchrotron outflow from the nucleus and two large lobes with a total NGC 3367 is a nearby barred galaxy that is classified as projected extent on the sky (from NE to SW) of 12 kpc, SB(rs)c in the Third Reference Catalog of Bright Galaxies (de resembling a radio galaxy. The axis of the ejected outflow Vaucouleurs et al. 1991, hereafter RC3) and as Sy 2-like, H ii in is highly inclined with respect to the axis of rotation of the Veron-Cetty´ & Veron´ (1986). Mid-infrared Spitzer observations disk (Garc´ıa-Barreto et al. 1998, 2002). Single-dish H i content 9 of NGC 3367 reveal the presence of [Ne v] lines at 14.3 μm of MH i ∼ 7 × 10 M has been reported for this galaxy and 24.3 μm with X-ray luminosity dominated by a power law (Huchtmeier & Richter 1989) and a high fraction of molecular with 2–10 keV luminosities of 2.0 × 1040 erg s−1 (McAlpine gas has been found mostly concentrated in the central 27 (r = 9 et al. 2011). NGC 3367 is located in the field of the Leo 5.7 kpc) M(H 2) = 2.7 × 10 M (Garc´ıa-Barreto et al. 2005). Group but it belongs to the background based on its optical NGC 3367 also shows weak thermal radio continuum emission −1 velocity of vo = 2998 km s and the mean velocity of the Leo (at 4.5 angular resolution) extended throughout the disk (Garc´ıa- I Group = 900 km s−1 (Ferguson & Sandage 1990; Stocke et al. Barreto et al. 1998) and Hα Fabry–Perot observations indicate 1991; Tonry et al. 2001). The closest candidate for a galaxy that its rotation axis lies projected on the disk at a P.A. of 141◦, companion is NGC 3391 at a projected distance of ∼ 563 kpc the N side of that projected line being closer to the observer or 18 optical diameters away (Garc´ıa-Barreto et al. 2003) and (Garc´ıa-Barreto & Rosado 2001). a recent search for isolated galaxies in the local universe based Despite the fact that several properties of NGC 3367 some- on the SDSS has also confirmed that NGC 3367 is an isolated how resemble a gravitational interacting system with another galaxy (Hernandez-Toledo´ et al. 2010). The optical appearance galaxy, there is still no supporting evidence. This is the first of NGC 3367 is dominated by a bright bar and an apparent paper in a series where we present our multi-wavelength data large-scale asymmetry or lopsidedness to the southwest side. and discuss some alternatives to the origin of the observed morphology and asymmetries. Our paper is split into two general parts: one describing the observations and the estimate of the ∗ Based on data obtained at the 0.84 m, 1.5 m, and 2.1 m telescopes of the galaxy parameters and the second discussing the interpretation Observatorio Astronomico´ Nacional, San Pedro Martir´ operated by the Instituto de Astronom´ıa, Universidad Nacional Autonoma´ de Mexico.´ of measurements as constraints to the recent dynamical history

1 The Astronomical Journal, 142:182 (17pp), 2011 December Hernandez-Toledo´ et al. in NGC 3367. Specifically, a description of observations and the calibration of the JHK system was performed using the U.K. techniques used in the data reduction are briefly described in Infrared System (Hunt et al. 1998). The sky conditions were Section 2. In Section 3, we present a brief summary of the main almost photometric with a typical seeing FWHM of 2 arcsec. morphological features found in the optical and NIR images. A We also dispose of VLA H i data coming from the NRAO VLA surface photometry analysis is carried out in Section 4, includ- archive, originally obtained in 2001 with the C-configuration. ing (1) an analysis of the surface brightness (SB) and color pro- We produced a full Natural Weighting data cube in order to files; (2) a coupled one-dimensional–two-dimensional (1D–2D) improve the sensitivity. Our final data cube has 63 channels and bulge/disk and bulge/bar/disk decomposition into Sersic,´ Ex- a beam size of 18.7 × 15.6 arcsec. We fully describe the H i data ponential, and Ferrer components. Section 5 presents different reduction in a forthcoming paper (Bravo-Alfaro et al. 2011, in bar properties like interstellar medium (ISM) shocks based on preparation). the dust lane geometry revealed by a B − I color map, a quantifi- cation of the bar strength and length, and a brief discussion of the 3. GENERAL MORPHOLOGY bar nature in terms of the Athanassoula & Misiriotis (2002) mod- The morphology of the galaxy in the optical and NIR bands els. In Section 6, lopsidedness is reviewed from various estima- is shown in Figure 1. Filter-enhanced versions in each band tors, namely, the concentration–asymmetry–clumpiness (here- are also presented (right-hand side), where the sky has been after CAS) parameters in the optical and near-infrared (NIR) = subtracted and the images have been Gaussian-filtered and then bands, the m 0–2 Fourier NIR and Hα amplitudes, and the subtracted from the original image to enhance both internal and Very Large Array (VLA) H i asymmetry from the moment 0 dis- external structures in the form of star-forming regions, structures tribution and the corresponding H i line profile. In Section 7,we embedded into dusty regions, or faint outer details of particular look for (1) evidence of low SB features likely related to a tidal interest for our discussion. origin and (2) the presence of recent galaxy accretion events or The bluer bands highlight a sharp semi-circular outline in the satellite companions in the observed colors. Section 8 presents N–W–S direction. This structure presents a complex pattern of a general discussion of the origin of the disk lopsidedness. We arms at a radius of about 50 arcsec (10 kpc) from the center. use Fabry–Perot Hα and H i VLA data to discuss possible ev- The arms in the inner region almost coalesce to form an internal idence of anisotropic gas accretion and its possible connection ring. Some bright H ii regions are strung along the inner parts to the active galactic nucleus (AGN) activity in NGC 3367. Fi- of two major arms that begin at the ends of the bar, these arms nally, our summary and concluding remarks are presented in = −1 −1 experiencing various levels of winding and branching. Section 9. A distance of 43.6 Mpc (Ho 75 km s Mpc )is The contrast produced by the filter-enhanced images enables adopted for NGC 3367 (Tully 1988), resulting in a linear scale −1 us to (1) visualize fainter structure beyond 50 arcsec (10 kpc) of 210 pc arcsec . in the form of fragmentary structures at the north and along the external border of the outline (U-to-R-band images) but also 2. OBSERVATIONS AND DATA REDUCTION offers hints of the more circular nature of the external disk (R The optical UBVRI observations were carried out at the and I bands) and (2) emphasize a falloff of the SB at about 0.84 m telescope of the Observatorio Astronomico´ Nacional at 50 arcsec (U, B, and V bands) that is observed to occur not with San Pedro Martir´ (OAN-SPM), Baja California, Mexico,´ with the same abruptness in the western side as in the northeastern a Site1 CCD detector yielding a total field of view of 7.2 × side. 7.2 arcmin and typical seeing FWHM values of 1.8 arcsec. A The NIR band images show the prominence of the bar as detailed description of the optical observations and the standard it is clearly enhanced by a dominance of an old population of data reduction within the IRAF platform5 can be found in stars in that region. There are also some localized high SB knots Garc´ıa-Barreto et al. (2007). The routines under the Space in the eastern end of the bar, perhaps evidencing the presence, Telescope Science Data Analysis System (STSDAS) were used depending on their age, of either a non-negligible population of in the reduction and analysis of both the optical and near-IR data. asymptotic giant branch stars or red giant and supergiant branch In this paper, a further processing of the images in 2 × 2 binning stars there. Note, as shown in Figure 2 below, that the typical − ∼ −2 mode was applied to have a pixel scale of 0.85 arcsec pixel 1, depth of the NIR images is 21 mag arcsec while that of the ∼ −2 similar to that in the near-IR observations. optical images is 23–24 mag arcsec at 60 arcsec from the The near-IR observations were carried out using the CAMILA center, respectively. This is a relevant issue, especially when instrument (Cruz-Gonzalez´ et al. 1994) at the OAN-SPM discussing properties of the external disk. 2.1 m telescope. The CAMILA instrument uses a NICMOS 3 4. SURFACE PHOTOMETRY ANALYSIS detector of 256 × 256 pixel format. The instrument was used in the imaging mode with the focal reducer configuration 4.1. Surface Brightness and Color Profiles f/4.5 in all our observations, resulting in a spatial scale of 0.85 arcsec pixel−1 and a total field of view of 3.6 × 3.6 arcmin. Azimuthally averaged radial SB profiles have been obtained The imaging observations were carried out using the broadband from our optical UBVRI images (see Garc´ıa-Barreto et al. 2007) J, H, and K filters. Each observation consisted of a sequence and from our NIR images as an initial characterization of of object and sky exposures, with the integration time of an NGC 3367 structure. Ellipse fitting to the isophotes was used to individual exposure limited by the sky counts, which was kept estimate radial profiles of intensity, ellipticity (), and position well below the nonlinear regime of the detector. The final angle (P.A.). The ellipses were calculated using the routines exposure times on NGC 3367 were 23, 11, and 21 minutes under the STSDAS package. Prior to profile extraction, the for the J, H, and K bands, respectively. The photometric FWHMs of stars in all the images were matched to the one having the poorest seeing (2.3 arcsec). The SB profiles were extracted using ellipse fitting with a fixed center. In order to 5 IRAF is distributed by the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., assure a homogeneous computation of structural parameters and under cooperative agreement with the National Science Foundation. color gradients, we use the R-band external isophotes as input

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U B

1’

V R

I J

H K

Figure 1. U-toK-band images of NGC 3367 and their corresponding ﬁltered-enhanced versions (adjacent right-side images). The scale of the images is illustrated in the U-band image. All images are oriented according to the astronomical convention; north is at the top and east is to the left.

14 5 NGC 3367 16 4 B-K 18 3

20 K 2 B-I J J-K 22 1 R J-H B-V 24 0 U 26 -1 0204060 0204060

0.8 U 0.8 J B K 0.4 0.4 0 0 60 60 0 0 -60 -60 0204060 0204060 RADIUS (arcsec) RADIUS (arcsec)

0.2 R External Region 0.1 0 80 40 0 60 80 100 RADIUS (arcsec) Figure 2. Surface photometry of NGC 3367. Upper panels: the U-toK-band surface brightness profiles and color profiles. Middle panels: ellipticity and P.A. radial profiles for U, B, J,andK bands. Lower panel: external ellipticity and P.A. radial profiles from a deep R-band image. The vertical lines in each panel indicate the end of the bar and the position of the truncation radii (from the optical images), respectively.

3 The Astronomical Journal, 142:182 (17pp), 2011 December Hernandez-Toledo´ et al. parameters to determine the SB profiles in UBVIJHK bands. is within the reported range of values coming from different We trace SB profiles up to ∼23–25 mag arcsec−2 in optical methods, as discussed in Garc´ıa-Barreto & Rosado (2001) and bands and ∼21–22 mag arcsec−2 in the NIR bands. These levels more recently, from a kinematic analysis using various gas correspond to conservative SB errors of ∼0.12 mag arcsec−2. tracers (M. Cano-D´ıaz et al. 2011, in preparation). The results of the surface photometric analysis are plotted in Figure 2. To avoid crowding, the SB and color profiles for a 4.2. 1D–2D Bulge/Bar/Disk Decomposition few wavelengths are plotted. Two dashed vertical lines in each panel indicate, from left to right, the end of the bar and the Although NGC 3367 has a prominent stellar bar, a common position of the NE SB falloff, respectively. The middle panels approximation is to perform a bulge/disk decomposition to an show the corresponding ellipticity and P.A. radial profiles aimed azimuthally averaged 1D profile (in fixed P.A. and mode) that to illustrate the difficulties behind a correct identification of the smooths out the bar as well as the spiral arms in the profile bar properties as a function of wavelength also in the presence extraction. In a first-order approach, we fit the radial intensity of prominent knots at both ends of the bar (see Figure 1). The profiles with a composite profile containing a Sersic´ bulge and lower panel shows the external ellipticity and P.A. radial profiles an exponential disk. Our algorithm splits 1D galaxy luminosity of NGC 3367 estimated from an additional deep R-band image profiles into bulge and disk components simultaneously by using (see Figure 11 below) that was built from the sum of our various a nonlinear Levenberg–Marquardt least-squares fit (Press et al. R-band exposures adding up to a total of 1.4 hr of exposure, 1992) to the logarithmic intensities. Seeing effects are accounted useful for estimating a representative geometry for the external for by convolving the theoretical bulge-disk SB profiles with a disk. radially symmetric Gaussian point-spread function (PSF). The upper left panel of Figure 2 shows a systematic flattening In the upper-left panel of Figure 2, note that the shape of of the SB profiles as we go from K to U bands. This behavior the U-band SB profile resembles a truncated Freeman type II could be interpreted as a signature of an optically thick disk at profile. However, that shape practically disappears at longer the central regions becoming mildly transparent at large radii wavelengths in the NIR bands. This fact combined with the (Evans 1994). The flattening in the SB profile is correlated high central CO emission reported by Garc´ıa-Barreto et al. with a color gradient showing that the disk becomes gradually (2005) suggests that extinction may play a significant role in bluer at outer radii. A red bump in the color profiles reaches as the gradual change of the SB profile across wavelengths. We redas4.5magin(B − K) in the first few arcseconds and did not take into account that apparent truncation in the U and B decreases to about 4 mag at about 17 arcsec which corresponds bands. Instead, we homogenized the 1D fits by using the same to the end of the stellar bar (first vertical dashed line). The peak radial zones (up to 55 arcsec) in all the U-toK-band profiles of the red bump is consistent with the maximum concentration of and then the fitting was carried out. At this stage, our results CO emission (Garc´ıa-Barreto et al. 2005). In the external region indicate that the bulge is exponential in all the observed bands of the SB profile we notice a turnover or possible disk truncation (Sersic´ n = 0.9–1.1). at ∼55 arcsec (second vertical dashed line), this truncation being Next, our images were prepared to run a set of 2D fitting more evident in the optical than in the NIR bands. Van der algorithms (GALFIT; Peng et al. 2002, 2010). For that purpose, Kruit (1988) proposed that many stellar disks may possess radial the fitting region, sky background, PSF image, and pixel noise cutoffs at approximately the same location as seen in the star map were all estimated and generated. In the first step, we formation (SF) regions. Figure 1 shows that this turnover is coupled our 1D method to GALFIT by feeding the results of visible at approximately the same position corresponding to a our 1D fits and the STSDAS isophotal analysis (n Sersic´ index, radius where the abrupt falloff in SF is appreciated. axial ratio, position angle, and boxiness/diskiness parameters; The bar ellipticity was measured as the maximum of the see Figure 2) as priors to model a 2D generalized Sersic´ bulge ellipticity within the bar region while the bar length was and an exponential disk (in free fitting parameter mode) just measured at the transition region between the bar and the disk similar to our 1D case. Figure 3 shows our best 1D fit to the where both the ellipticity and P.A. change significantly. A set of K-band SB distribution (left panel) as well as the residual image high SB knots precisely at the NE and SW ends of the bar were of NGC 3367 after subtracting the best 2D bulge/disk fit (right identified as the dominant sources influencing a correct estimate panel). The results for the disk and the exponential bulge (Sersic´ of the bar ellipticity and P.A. Similarly, in the external regions, n = 0.9–1.2) are consistent with our 1D fits. However, relatively another set of high SB knots along the N–W–S outline were poor χ 2 values were obtained in all cases. identified as the dominant features influencing a correct estimate In the second step we carried out a higher order analysis of the geometry of the disk. Instead of letting the ellipse-fitting including a Ferrer’s bar in addition to the bulge and disk routines run blindly, we carefully masked all the prominent components. The Ferrer’s bar (Binney & Tremaine 1987) has knots and implemented an interactive routine to superpose each a nearly flat core and an outer truncation. The sharpness of the isophote onto the corresponding images, enabling a visual check truncation is governed by a parameter α, whereas the central of the masking performance and the correct estimate of the bar slope is controlled by a parameter β. This profile is defined parameters. up to an outer radius rout beyond which the profile has a The bar length in the K band converged to r ∼ 17 arcsec, value of 0. Our procedure assumed both the representative 1D corresponding to a diameter of ∼7 kpc at the distance of isophotal parameters within the bar region (see Figure 2) and NGC 3367. Similarly, the observed P.A. of the bar is 66◦ ± 4◦, the parameters obtained in the bulge/disk 2D fitting as priors. both quantities in agreement with other estimates (Garc´ıa- A simultaneous fitting of the bulge and the disk followed by Barreto et al. 1996, 1998). A representative ellipticity of the bar the inclusion of the bar as well as a simultaneous fit to the (corrected for inclination) in the J and K bands is max = 0.58 disk and the bar, followed by the bulge fitting, were considered. ±0.05. Finally, from the lower panel in Figure 2, we adopt a The best values of α = 0.5–0.7 and β = 1.89–1.96 of the nominal radius of 80 arcsec (∼3.2 R-band disk scale lengths) to Ferrer’s bar for a fixed truncation radius (rout = 16 arcsec) estimate an inclination of 25◦ ± 5◦ for NGC 3367. This value yielded disk parameters consistent with the ones found in our

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Figure 3. Left panel: best 1D Sersic´ + Exponential fit to the K-band surface brightness profile. Right panel: residual image after subtracting the best 2D Sersic´ + Exponential fit. Lower-right panel: residual image after subtracting the best 2D Sersic´ + Bar + Exponential fit. (A color version of this figure is available in the online journal.) previous 1D–2D bulge/disk decomposition but with a bulge n Do bars contain information about the strength of secular Sersic´ index between 1 and 1.8 and re ∼ 2.5–5 arcsec. Figure 3 evolution? Bars may drive spiral density waves (Kormendy & (lower-right panel) shows the residual image of NGC 3367 Norman 1979), generate resonance rings of stars and gas (Buta after subtracting the best 2D bulge/bar/disk fit (χ 2 ∼ 1). The & Combes 1996), change abundance gradients (Martin & Roy residuals show almost no bar resemblance and still an intricate 1994), or induce gas inflow that may lead to bar weakening and nuclear structure. A possible explanation is that the bulge has bulge growth (Norman et al. 1996). non-regular structure, perhaps an unresolved circumnuclear structure as suggested by the (B − V) pixel map in Figure 12,in 5.1. Dust Lanes addition to a central point source (AGN) that was not included B I in the GALFIT models. Note that the bar residuals may suggest The structural differences between - and -band images can a bar horizontal bending mode, not included in our analysis. be used to map the SF and dust distributions. Figure 4 shows Another possible source for the residuals could be related to the a close-up of the inner region of NGC 3367 as seen through a B − I dust distribution in the inner regions of NGC 3367. Note also color map. Dark regions represent redder colors. A dust that the spiral arms are not heavily important inside one disk lane, conspicuous in this color map, can be appreciated as a scale length and thus were not modeled. The range of n Sersic´ dark curved feature running from east to west of the nucleus. / indices found for the bulge suggest B/D ratios ranging from The nucleus and part of the bar arms can also be appreciated 0.07 to 0.11. as gross bluer features. The dust lane appears slightly offset Our results assess the likelihood of a pseudo-bulge in from the bar major axis toward its leading edge. Dust lanes NGC 3367 consistent with an exponential luminosity distri- are caused by building up of gas at shocks (Prendergast 1966, bution in all the observed wavelengths, contrary to a classical 1983; van Albada & Sanders 1982; Athanassoula 1992). Dust bulge structure as suggested by Dong & De Robertis (2006). lanes are closely linked to the bar mass, potential ellipticity, and The presence of a strong bar in this galaxy requires that a pure pattern speed. Athanassoula (1992) has modeled systematically bulge/disk fitting procedure be greatly influenced by the radial the ISM response in disks to stellar bars scanning different range over which the fitting is done, causing (depending on the masses, structure, and angular speed, concluding that shocks adopted parameters) possible overestimates of the bulge. It is strength and location are useful for inferring the bar physical thus important to consider the bar to characterize the bulge of properties (Weiner et al. 2001). The dust lane curvature observed NGC 3367. in Figure 4 when compared with the results of Athanassoula (1992) suggests that the bar in NGC 3367 might be either weak 5. BAR DISSECTION or not as fast as the ones found in early-type galaxies which are lines parallel to the bar major axis. As a reference, Salo et al. The evolution of galaxies in later stages of the universe may (1999) presented one of the largest collection of Ωp estimates be governed by slow secular processes, related to collective for 38 OSUBSGS spiral galaxies (Rautiainen et al. 2008), dynamical phenomena, such as bars, spiral arms, or the dark concluding that the pattern speed of the bar depends roughly matter halo response to baryons (Kormendy & Kennicutt 2004). on the morphological type. The average value of corotation

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(B − I) 8

15 ’’ 4

− Figure 4. Close-up of the inner region of NGC 3367 as seen through a B I color 3 map. Dark regions represent redder colors. The dust lane can be appreciated as a -20 -10 0 10 20 dark curved feature running from east to west of the nucleus. It appears slightly offset from the bar major axis toward its leading edge. 1 = 210 pc. The nucleus Figure 5. K-band intensity profile along and perpendicular to the bar (dashed and part of the arms are appreciated as gross bluer features. and solid lines, respectively). The central peak shows the unresolved nucleus. Peaks in the profiles located at around 4 kpc show the position of spiral arms, which are asymmetric. At 6 kpc the profiles reach a ring. Beyond 10 kpc the resonance radius to bar radius, R, increases from 1.15 ± 0.25 profiles in orthogonal directions are similar, suggesting that the disk is close to in types SB0/aSBab to 1.44 ± 0.29 in SBb and 1.82 ± 0.63 axisymmetric. in SBbcSBc types, similar in type to NGC 3367. While the (A color version of this figure is available in the online journal.) curved dust lane morphology in Figure 4 might be consistent with NGC 3367 having a relatively slow bar, it is known that by Faber & Gallagher (1979) for late-type spiral galaxies (see this diagnostic is degenerated and a weak bar can trigger curved also Bershady et al. 2010). dust lanes (Athanassoula 1992). On the other hand, Gabbasov In particular MH models show a flat SB profile along the et al. 2009 recently applied the Tremaine & Weinberg (Tremaine bar major axis. Evaluating that situation for NGC 3367 is more & Weinberg 1984) method to a set of Fabry–Perot Hα gas complex because of the multiple spiral arms. In Figure 5,we observations in NGC 3367 finding a value of Ω = 43 ± 6, p can see that there is a lack of a flat feature in the profile making consistent with a fast bar (R 1.4). Although currently we do the MH model unlikely. In order to decide between MD and not have enough data to sort out this apparent contradiction, a MDB models, we must also compare Figure 3 in Athanassoula forthcoming paper (M. Cano-D´ıaz et al. 2011, in preparation) & Misiriotis (2002) with images in our Figure 1. Although the will treat this issue. bar in NGC 3367 is strong (see section below), it is by no means similar to the one in MH models, however, it is also not as 5.2. Bar Shape and Nature round as the bar in an MD model. We tentatively conclude that the NGC 3367 bar is closer to MDB models, but because of Figure 5 shows intensity profiles along the major and minor the negligible bulge inferred from our B/D analysis, Figure 5 axes of the bar. Athanassoula & Misiriotis (2002) have suggested could be evidence of a subdominant dark matter mass inside that the bar structure is sensitive to which is the dominant an exponential length. Note that in this interpretation the halo galaxy component exchanging angular momentum with the bar contribution is not negligible to the one from the disk; this is itself. They introduce the following nomenclature for profiles not unreasanable because Halo Adiabatic Contraction models along the bar major axis: halo (MH)/disk (MD)/disk–bulge predict a similar structure (Klypin et al. 2002; Gnedin et al. (MDB) in their Figure 5. The characters in parentheses indicate 2004;Col´ın et al. 2006). Although it is possible to argue that dust the dominant structure in the bar region, namely, a centrally extinction is masking a light profile truly closer to an MD model, concentrated halo (MH), a less centrally concentrated halo or note, however, that not only the K-band but even the 3.6 μ images disk (MD), or a bulge and a non-centrally concentrated halo or from Spitzer (N. Z. Scoville 2008, private communication) bulged disk (MDB), for instance, which indicates the structural support our conclusion that the MDB model better represents component dominating the angular momentum extraction out the surface density profile. A stronger assessment of the result from the bar. Since NGC 3367 is a low-inclination galaxy ◦ requires re-examination including stellar population and dust (∼25 , see Section 4.1), projection effects are not considered radiative transfer analysis and also considering bar properties in as an important systematic for assigning a morphological bar an accreting galaxy. type from the intensity profiles. However, it is important to mention that a direct comparison of theoretical predictions with 5.3. Bar Strength NGC 3367 is subject to knowing M/L gradients and also any dust effect. We minimize the latest by using K-band images and The evolution caused by bars in disk galaxies is due to gravity adopting a ratio of M/L ∼ 1, consistent with the values reported torques. Any disk asymmetry like a bar or spiral mode gives

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Table 1 The J-, H-, and K-band Bar Strength in NGC 3367

max Band QT (R) J 0.43 ± 0.05 H 0.44 ± 0.06 K 0.44 ± 0.09 rise to tangential forces in addition to radial forces, and then to gravity torques. The computation of the gravitational torques provides important information about the average strength of the perturbing potential. Combes & Sanders (1981) suggested that these torques could provide a useful way to quantify non-axisymmetric features’ strengths if the potential could be estimated. The potential can be estimated from de-projected NIR images by solving Poisson equations, for example, using Fourier transform techniques, along with assumptions concerning mass- to-light ratios and vertical density distributions (Quillen et al. 1994). From this potential, the radial and tangential components of the forces in the plane of the galaxy can be estimated. Following these ideas we estimate the bar strength in NGC 3367 by using the following equation (Combes & Sanders 1981;Buta & Block 2001): F max(R) Q R = T , T ( ) (1) Figure 6. Tangential to average radial force ratio map for NGC 3367. The color FR(R) code illustrates regions that, depending on quadrant relative to the bar, can be max = Φ negative (blue clouds) or positive (red clouds) due to the change of sign of the where FT (R) 1/R[∂ (R,θ)/∂θ]max represents the max- tangential force. The maximum values of the ratio in the red clouds are of the imum amplitude of the tangential force at radius R and order of +0.42. The maximum values in the upper-left blue cloud are −0.51, FR(R) =(dΦ0/dR) is the mean axisymmetric radial force while those in the lower-right blue cloud are −0.42. Note the asymmetry in the at the same radius, derived from the m = 0 component of the color distribution along the quadrants. The contours from an R-band image are gravitational potential. The potential Φ is estimated by using overplotted. the NIR images, assuming a constant (M/L) ratio across the (A color version of this figure is available in the online journal.) disk. Then the potential in two dimensions can be derived as the convolution of the mass density with the function 1/R using fast Fourier transform techniques (Binney & Tremaine 1987, p. 90). max = = The gravitational torque is a function of R, but the maximum a mean value of QT (R) 0.44 for hz 325 pc. This value of QT (R) can provide a single measure of bar strength value places NGC 3367 in the borderline between classes 4 for a whole galaxy, if the gravitational potential is known. and 5 of Buta & Block bar-strength classification scheme. Table 1 shows the estimates of QT (R) for NGC 3367 from In that study, classes 1, 2, and 3 indicate a weak bar, while the J-, H-, and K-band images. In our analysis we adopt hz = only a small fraction of the galaxies have a bar class = 4 325 pc, which is the exponential scale height of our Galaxy or larger suggesting that NGC 3367 can be considered as a (Gilmore & Reid 1983). The study by de Grijs (1998) indicates galaxy with a strong bar. This strong gravitational torque could that late-type galaxies on average have a thinner disk than earlier be the source of secular evolutive processes. The significant type systems. To account for possible variations in scale height increase in molecular gas mass toward the central regions of and for the possibility that some bars are thicker than their disks, NGC 3367 as reported by Garc´ıa-Barreto et al. (2005) could we have made separate potential runs for hz = 225 and 425 pc. be related to such processes. Secular scenarios invoking bar Figure 6 shows the ratio map for NGC 3367 (hz = 325 pc) with formation or dissolution and bulge formation (possibly related the contours from an R-band image overplotted. to the presence of nuclear activity) might be viable mechanisms Figure 6 shows the characteristic pattern of a bar with four for the evolution of isolated galaxies along the Hubble sequence well-defined regions where the ratio, depending on quadrant (Bournaud & Combes 2002). relative to the bar, can be negative or positive due to the Alternatively, bars can be characterized as strong when they change of sign of the tangential force. The color coding is have large ellipticities or the tangential forces are large. As useful to visualize the differences that exist in Q by quadrant. the orbital families of bars strongly depend on the underlying These differences may be explained either by the presence gravitational potential, a correlation between the ellipticity and of the inner spiral arms enclosing the bar (see Figure 1)or the tangential force is expected (Laurikainen et al. 2002;Buta by some intrinsic asymmetry in the bar itself that could make et al. 2004). We have compared our de-projected bar ellipticity max these regions unequal. Table 1 in Buta & Block (2001) defines in NGC 3367 with that predicted from the QT (R) – relation the bar strength classes that we adopt in our study. NGC 3367 in Laurikainen et al. (2002). A consistent bar strength estimate approximately retains its bar strength class independently of could be obtained. The fact that we can directly measure the scale height variations from 225 to 425 pc. We find that an bar strength and also the pattern speed opens the possibility of uncertainty of ±100 pc in hz produces an average uncertainty accurately estimating the central stellar M/L. We are exploring of ∼5%–10% in bar strength. We report that the maximum that possibility in a forthcoming paper (M. Cano-D´ıaz et al. tangential force reaches 44% of the mean radial force with 2011, in preparation).

7 The Astronomical Journal, 142:182 (17pp), 2011 December Hernandez-Toledo´ et al.

-0.1 0 SaSb 0.1 SbcSm 0.2 0.3

0.4 SaSb SbcSm 0.5 0.6 0.7 0.8 0 0.2 0.4 0.6 0.8 1 0 SaSb Isolated Spirals 0.2 Interacting Spirals (S+S) SbcSm SaSb 0.4 SbcSm Starburst ULIRGs 0.6 NGC 3367

U R K 0.8 B I

1 V J 5432

Figure 7. CAS parameter space and the loci of NGC 3367. The UBVRIJHK symbols indicate its wavelength-dependent position. Black boxes show the maximum variation of the observed CAS parameters from B to K band for a sample of isolated galaxies of Sa–Sb and Sbc–Sm morphological types (Hernandez-Toledo´ et al. 2007;Hernandez-Toledo´ & Ortega-Esbr´ı 2008). Barred circles show the expected loci for interacting (S+S) pairs (Hernandez-Toledo´ et al. 2005). The expected loci for starbursts and ULIR galaxies is taken from C03. (A color version of this ﬁgure is available in the online journal.)

6. LOPSIDEDNESS 6.1. CAS Structural Parameters

Next we present a quantitative analysis of the asymmetry Figure 7 shows the wavelength-dependent position of properties of NGC 3367 in various wavelengths. We start with NGC 3367 in the CAS parameter space (UBVRIJK sym- the analysis of the optical and NIR light by means of the CAS bols). The loci (average and its standard deviation) for a parameters. These three structural and morphological indices sample of isolated Sa–Sb and Sbc–Sm galaxies (Hernandez-´ constitute the so-called CAS system, which has been proposed Toledo et al. 2007;Hernandez-Toledo´ & Ortega-Esbr´ı for distinguishing galaxies at different stages of evolution 2008)intheR-band CAS planes are indicated as crosses (Conselice 2003, hereafter C03 and references therein). Briefly, and continuous error bars. The solid boxes indicate the the concentration index C is defined as the ratio of the 80%–20% maximum amplitude of variation (lower and upper limits) of curve of growth radii (r80, r20) within 1.5 times the Petrosian the CAS parameters from B to K bands for the isolated disk inverted radius at r(η = 0.2) r normalized by a logarithm: sample. For comparison, the R-band CAS averages and stan- C = 5log(r80/r20). The concentration of light is related to the dard deviations of galaxies in interacting S+S pairs (open cir- galaxy light (or stellar mass) distribution. cles; Hernandez-Toledo´ et al. 2005), starburst (long-dash), and The asymmetry index is the number computed when a ultraluminous infrared (ULIR) galaxies (short-dash; C03) are galaxy is rotated 180◦ from its center and then subtracted also plotted. from its prerotated image. The summation of the intensities NGC 3367 experiences a strong migration in the CAS di- of the absolute-value residuals of this subtraction are compared agram. While the UBVR band CAS values place it as a with the original galaxy flux. This parameter is also measured typical starburst, the R band asymmetry (A(R) = 0.35) within r.TheA-index is sensitive to any feature that produces is also consistent with that of weakly interacting galaxies asymmetric light distributions. This includes galaxy interactions (Hernandez-Toledo´ et al. 2005) and at the end its locus in the JK and mergers, large star-forming regions, and dust lanes. bands place it within the boundaries of nearly isolated galaxies. Galaxies undergoing SF are very patchy and contain large The Population I disk of young stars (and dust) yield a significant amounts of light at high spatial frequency. To quantify this, the contribution to the optical U,B,V CAS distributions, making clumpiness index S is defined as the ratio of the amount of light their average values largely decoupled from the correspond- contained in high-frequency structures to the total amount of ing to older J,K stars. The clumpiness parameter S compares light in the galaxy within r.TheS-parameter, because of its the amount of light in star-forming clusters and young associa- morphological nature, is sensitive to dust lanes and inclination. tions to the light in a more diffuse older disk population. This

8 The Astronomical Journal, 142:182 (17pp), 2011 December Hernandez-Toledo´ et al. measure correlates with hydrogen recombination lines (Hα) and average value for field galaxies. The gradual change in phase in gives an indication of recent SF activity. We estimate the star that region denotes that such feature lies along an arm winding formation rate (SFR) in NGC 3367 through LFIR (see Table 2). upward to the north. Since the outer disk in the J band is weakly −1 −10 SFRFIR(M yr ) = 1.40×10 LFIR(L) (Devereux & Young detected, to visualize the behavior of A1 in the boundary of 1991) holds for the high-mass end (M 10 M) and was cor- 60 pixels and beyond, we use a deep R-band image instead, rected by the factor given in Devereux & Young (1990)totake obtaining that A1 appears to decrease below 0.05 level, with a into account the fact that LFIR is used instead of LIR. An SFR roughly constant phase. By comparison, the phase is nearly −1 −1 ∼3.1(M yr ) in NGC 3367 (compared with 5 (M yr )re- constant with radius in the data of Rix & Zaritsky (1995). ported by Garc´ıa-Barreto et al. 2005) is an order of magnitude NGC 3367 could be regarded as slightly non-symmetric, at the −1 higher than the median value SFR ∼ 0.27(M yr ) obtained for nominal intermediate radii. In the lower panel of Figure 8,the a sample of isolated galaxies of similar (Sc) morphological types m = 2 amplitude and phase confirms the existence of the bar (Hernandez-Toledo´ et al. 2001), consistent with NGC 3367 be- within 1.0 Rd. Between 1.0 Rd and 2.0 Rd there is another local ing in the starburst region of the CAS diagrams. maximum of similar amplitude, that according to the associated phase, corresponds to the inner arms enclosing the bar. 6.2. NIR Lopsidedness (Fourier Analysis) The light distribution in many galaxy disks is non- 6.3. Hα Lopsidedness axisymmetric or lopsided with a spatial extent much larger along Figure 9 shows the results of the Hα Fourier Am(R)/A0(R) one half of a galaxy than the other. Nearly 30% of galaxies have m = 1–2 amplitude and phases estimated from an image significant lopsidedness in stellar disks with an amplitude of = resulting after collapsing the 48 channels of a Fabry–Perot Hα >10% measured as the Fourier amplitude of the m 1 com- data cube (Garc´ıa-Barreto & Rosado 2001). ponent normalized to the average value (Rix & Zaritsky 1995; TheasymmetryinHα is presented at about the same radial Zaritsky & Rix 1997; Bournaud et al. 2005). = = distance as that in near-IR study (1 pixel 0.6 arcsec). The We calculated the azimuthally averaged m 0, 1, and 2 two tracers show qualitatively similar features in the m = 1, 2 Fourier amplitude profiles (A0, A1 and A2) in NGC 3367, modes, except for the significantly higher amplitude observed following the prescription described by Rix & Zaritsky (1995) in the Hα tracer. In the 80 pixel (∼50 arcsec) region the Hα in the NIR light. The SB distribution μ(R,φ) can be expressed m = 1 phase reveals the prominence of the N–W–S outline that as a Fourier series: dominates the global Hα appearance of NGC 3367 as devised ∞ in the left panel of Figure 9. This is in line with the results im[φ−φm(R)] μ(R,φ)/μ(R) = Am(R)e , (2) of Jog (1997), who claims that in a galactic disk, a lopsided m=1 distribution should induce an azimuthal asymmetry in SF. For the m = 2 mode, similar to the m = 1 case, a significant increase where φ denotes the azimuthal angle, m is the azimuthal number, in amplitude is also observed. NGC 3367 is locally and globally and Am and φm(R) are the associated Fourier amplitude and more asymmetric in the Hα light than in the NIR wavelengths. phase, respectively. The isophotal SB at radius R is given by μ(R) . 6.4. H i Lopsidedness Each filter image was re-binned onto an (R,φ) grid, using 30 bins in radius and 24 bins in azimuth. We have fixed a The frequency of asymmetries among spiral galaxies has minimum radius of 4 pixels and a maximum radius of 60 pixels. alternatively been estimated from the global H i profiles of Note that we quote the analysis in the NIR images to 60 pixels a large sample of field galaxies (Richter & Sancisi 1994). corresponding to a maximum radius of 51 arcsec, shorter than Examples of asymmetric global H i profiles can be found in those in the optical images, but still ensuring enough signal in M101 and NGC 4395. About 20% of the systems examined the disk emission at the J, H, and K bands. showed strong asymmetries and up to more than 50% of the Figure 8 shows the results of Am(R)/A0(R)forthem = 1–2 whole sample showed some mild asymmetries. That result modes in the J band. Radius is plotted in pixel units (1 scale has been confirmed by a 21 cm H i survey of 104 isolated length = 22.54 pixels or 19.16 arcsec). The scale length was galaxies with the Green Bank 43 m telescope (Haynes et al. calculated by fitting a straight line in the disk domain in the 1998) and also by more recent observations which image A0(R) Fourier amplitude (upper panel; which formally represent the H i distribution and the kinematics of a large sample the mean light profile) consistent with the values estimated from of galaxies (Westerbork H i Survey of Spiral and Irregular our former SB profile fittings. The intermediate and lower panels Galaxies, WHISP). At least one-half of nearly 300 objects from show the m = 1 and m = 2 amplitudes and their corresponding WHISP shows some lopsidedness either in the H i distribution, phases, respectively. in the kinematics, or in both. It should be noted that these As can be seen, the NIR observations enclose light to almost lopsided galaxies seem to be in non-interacting systems and that, 3 Rd . The results for A1 are certainly different when we use therefore, the lopsidedness cannot be explained as a present tidal different regions to calculate the mean. For example, in the effect. In this paper we started the basic analysis of NGC 3367 inner disk, up to 1.0 Rd,theA1 distortion is weak (0.05 H i asymmetry properties. The upper panel of Figure 10 shows or lower), similar to that observed in other galaxies (cf. Rix a gray-scale H i intensity map obtained from the moment 0 & Zaritsky 1995). For radii between (1.5 Rd,2.5Rd), A1 = VLA data cube (natural weighting) showing various contours (0.12, 0.11, 0.11) for the J, H, and K bands, respectively, close above the sigma level. The lower panel shows the corresponding to the mean value (A1 =0.10) in the sample of 149 mostly integrated H i velocity profile. field galaxies in Bournaud et al. (2005). More specifically, The moment 0 intensity map shows (1) an H i hole between 1.0 Rd and 2.0 Rd there is a local maximum at 0.15 in the central region, mostly covered with molecular gas level that corresponds to a prominent knotty region near the (Garc´ıa-Barreto et al. 2005) and (2) an H i asymmetry in the northeastern end of the bar, a value that is higher than the column density with higher values at the northwest at good

9 The Astronomical Journal, 142:182 (17pp), 2011 December Hernandez-Toledo´ et al.

1 NGC 3367

0.5

-0.5

20 40 60

0.25 2 0.2

0.15 0 0.1 0.05 -2 0 20 40 60 20 40 60

0.25 1 0.2 0.15 0

0.1 -1 0.05 20 40 60 20 40 60

Figure 8. Amplitude and phase of Fourier m = 0–1, 2 modes in the J band. Radius is plotted in pixel units. The J-band scale-length = 22.54 arcsec (1 pixel = 0.85 arcsec).

Figure 9. Left panel: the moment 0 Hα image from the collapsed Fabry–Perot data cube. Right panel: the corresponding Hαm= 1, 2 Fourier modes. statistical significance. The shape of the global H i column den- sion line at the galaxy systemic velocity is consistent with the sity distribution when superposed on an optical image strongly excess column density in the northwest minor axis region (P.A. emphasizes that apparent truncation viewed not with the same major axis ∼51◦). abruptness in the western than in the northeastern side in the To estimate the H i asymmetry, we first computed the flux UBV and Hα images. The integrated VLA profile shows higher ratio f = F 1/F 2 between the two halves of the profile. We flux density in the redshifted side of the spectra, consistent with have taken the total width at 20% of the peak flux density, and the available single-dish H i velocity profiles for NGC 3367 in estimated both the extremities of the profile and its center. The the literature. The absence of a drop-off in the integrated emis- asymmetry parameter is defined as A = 10(1−F 1/F 2) yielding

10 The Astronomical Journal, 142:182 (17pp), 2011 December Hernandez-Toledo´ et al.

Figure 11. A1.4hrR-band logarithmic-scaled image of NGC 3367. The circle at ∼ 90 arcsec illustrates the position of the region with S/N = 3. (A color version of this ﬁgure is available in the online journal.)

et al. (2005) for galaxies in the local universe, indicating that in NGC 3367 H i asymmetry is detected with good statistical significance, regardless of the instrumentation. We also explored the VLA H i velocity channels. However, 100 at the current signal level we do not find convincing evidence of neutral gas fall or ejection. The fact that we find a significant NGC 3367 lopsidedness in the H i gas component in NGC 3367 suggest A = 10(1 - F1/F2) that the triggering event must have happened some time in the 80 A = 1.8 +- 0.7 past. In Section 8, we use gas relaxation time arguments in order to constrain the time of a perturbation event.

60 7. LOW SURFACE BRIGHTNESS STRUCTURES AND COMPANIONS The most natural explanation for NGC 3367 perturbed mor- 40 phology and asymmetries is a recent encounter with a low-mass galaxy. A deep 7.2 × 7.2 arcmin R-band image of NGC 3367 has been produced in order to look for low SB features reminis- cent of possible tidal interactions. The final image in Figure 11 20 F1 F2 is the sum of one 1800 s exposure, two 1200 s exposures, and one 900 s exposure and it is presented in logarithmic scale. The circular contour illustrates the position of regions with S/N = 3. This image highlights the more circular nature of the disk and 0 2800 3000 3200 some possible diffuse light structures at the outskirts. To quote the depth of the image we built a pixel representation of two Figure 10. Upper panel: the H i intensity map of NGC 3367 from the moment images dubbed as the variance and the average by combining 0 VLA data cube (H. Bravo-Alfaro et al. 2011, in preparation), superposed on all the images intervening in Figure 11. Since the calibration a u-band image. Lower panel: the corresponding integrated H i velocity profile. of this deep image is not currently available, we relied in The center, the extreme values at the 20% level, and the integrated flux of each our calibrated short exposure images (typically 15 minutes) H i horn F1 and F2 are used to estimate the H i asymmetry. in the same band, as shown in Figure 2. We estimate an S/N ∼ 3 at a maximum radius of the order of 80 arcsec a value A = 2.2 for NGC 3367. For comparison, note that in (see circular contour), with a detection limit at that position −2 the sample of moderately isolated galaxies in Bournaud et al. of μR ∼ 26.0 mag arcsec . That level is of the order of that in (2005) only 26% (18 out of 80 galaxies) have A>2. In order to recent studies looking for similar features in isolated galaxies characterize possible instrumental or telescope effects that can (Smirnova et al. 2010). We also applied histogram equalization artificially increase intrinsic H i asymmetries, we estimated the and unsharp masking transformations to the image similar to H i lopsidedness in NGC 3367 from integrated spectra retrieved recent studies (Mart´ınez-Delgado et al. 2010), however, because from other single-dish telescopes (Huchtmeier & Seiradakis of the low S/N beyond 80 arcsec, we find no reliable evidence for 1985 [Effelsberg]; Mirabel & Sanders 1988 [Arecibo]; Staveley- the existence of external low SB features at the current depth of Smith & Davies 1988 [Jodrell-Bank]; Springob et al. 2005 this image. A careful control of the background fluctuations due [Arecibo]), obtaining a mean value of A = 1.8 with a scatter of to flat-field residuals, internal reflections, ghosts, and scattered 0.7. Note that even the lowest estimated value is similar to the light that were not considered in detail in the present image average asymmetry (stellar component) reported by Bournaud deserves special attention. Deeper and careful observations are

11 The Astronomical Journal, 142:182 (17pp), 2011 December Hernandez-Toledo´ et al.

Figure 12. (B − V) color index map of NGC 3367 (upper left panel) and its pixel representation (upper right panel). Pixels are co-added as follows: blue (0 < (B − V ) < 0.5), green (0.5 < (B − V ) < 0.75), yellow (0.75 < (B − V ) < 1.0), red ((B − V ) > 1.0). (A color version of this figure is available in the online journal.) still necessary to provide unambiguous evidence of any tidal In the mean time, and with the above evidence, NGC 3367 is structure at the outskirts of NGC 3367 (Mart´ınez-Delgado et al. tentatively added to the list of candidate spirals showing various 2010). signs of perturbation, but no large nearby companions; these A procedure, coined as blinking colors, was implemented systems may have undergone minor mergers or some kind of to search for small companions within the disk and/or in the mass accretion during the past Gyrs. close neighborhood of NGC 3367. Under some circumstances, a small galaxy in front of a bigger one could still be rec- 8. DISCUSSION ognized if its own colors (stellar population; however, dust effects should be accounted for) are different enough from 8.1. Evidence for Recent NGC 3367 those in the background galaxy. To that purpose, we have Interaction with a Small Galaxy? produced various combinations of color index maps, namely, An intuitive explanation for NGC 3367 optical asymmetric U − B, B − V, U − K, B − K, from our U to K-band observa- morphology and large bipolar synchrotron emission might be tions, blinking the parent images along with their corresponding a recent merger with a small galaxy since NGC 3367 has no color maps with the hope of visually identifying any feature not large optical companion closer than 500 kpc (Garc´ıa-Barreto sharing the observed colors of the ground host galaxy. We also et al. 2003). A gas rich galaxy may be a suited candidate be- produced a pixel representation of each color map to have a more cause the asymmetric SF distribution. NGC 5548 is an example quantitative visualization of the color properties. Unfortunately of another Seyfert galaxy that is not suffering a major encounter, these procedures produced no positive detections. Figure 12 (left but that presents faint stellar structures remnant of past inter- panel) shows a (B − V) color-index map and the corresponding actions. Other important differences in this comparison are the distribution of pixels (right panel) within a radius of 60 pixels, galaxy morphological type and the high density environment in well within the disk and assuring a pixel S/N of 3. pixels were NGC 5548. Hence, finding evidence for a past possible merger binned to the order of the seeing and then corrected for galac- event in NGC 3367 is important in order to define a plausible sce- tic extinction. Blue color represents values (0 < (B − V ) < nario that explains its properties. A multiwavelength search was 0.5), pixels in green (0.5 < (B − V ) < 0.75), pixels in yellow performed in order to look for a possible remnant signature or (0.75 < (B − V ) < 1.0), and pixels in red ((B − V ) > 1.0). a dwarf perturber within the disk and in its close neighborhood. The color pixel representation suggests the existence of Initially we used our data at various optical Hα and infrared structure adjacent to the compact nucleus in the 0.75 < (B − wavelengths and different enhancing procedures, as presented V ) < 1.0 color range (the central green-yellow-red transition in Section 7. So far no convincing evidence was found, thus region in the upper right panel) resembling a circumnuclear placing constraints on the time of any possible galaxy accretion component. Whether there is a circumnuclear ring or disk is event. currently being assessed using archive Spitzer images and CO Different studies have analyzed galaxy disk response to minor kinematics and will be presented elsewhere (see also the residual mergers. For example, Kazantzidis et al. (2008) have recently image after our 2D bulge/bar/disk decomposition in Figure 3). studied the signature of galaxy merger histories in the context of Finally, we mention our search for Hα emission satellite ΛCDM scenarios mostly focusing in gravitational interactions galaxies in the close neighborhood of NGC 3367. A series of between existing thin galactic disks and small galaxies with narrow-band (Δλ ∼ 80 Å) Hα images with a field of view masses comparable to the LMC. They conclude that if a merging of 4.5 × 4.5 arcmin were obtained at the OAN-SPM 1.5 m event occurs, it could at least be responsible for the formation telescope with a set of extragalactic Hα filters tuned at different of thick disks, central bars, low SB ring-like configurations, redshifts (covering a radial velocity range from 1000 km s−1 and faint filamentary structures around a main galaxy, like in up to 6000 km s−1) and sharing a degree of velocity overlap NGC 3367, making this scenario compelling. Unfortunately among adjacent filters. A blinking of the images at different Kazantzidis et al. (2008) did not show the perturber remnant recession velocities with respect to that in the Gunn r broad distribution. In the following sections, we compare instead with band yielded no positive identifications. Recently James & Ivory similar experiments by Villalobos & Helmi (2008) because they (2011) showed that this kind of searches reveal star-forming present both the perturber satellite and the host disk distributions satellite galaxies. across different times. At the current state of our photometric

12 The Astronomical Journal, 142:182 (17pp), 2011 December Hernandez-Toledo´ et al. search we cannot support the idea of a recent minor merger with included satellite galaxies having total masses 10%–20% of that an LMC-like galaxy; at most we can constrain the event to the of the host galaxy disk, self-consistently modeled as a stellar distant past. Alternatively, if we consider a recent interaction component immersed in a DM halo. The stellar components with a dwarf galaxy, its mass should be considerably lighter have either a spheroidal or disky stellar structure. Particularly than NGC 3367 disk, otherwise narrow stellar streams may still interesting are the low SB shells, especially visible in the be detectable. outskirts of the final thick disks, that last for about 1.5–2 Gyr after the merger has been completed. Diagnosing the existence 8.2. Possible Origin of Disk Lopsidedness of these shells acquires relevance in the case of NGC 3367. If we compare with Figure 7 in Villalobos & Helmi (2008), NGC 3367 asymmetry properties were characterized using we see that there are not noticeable thin stellar structures after different techniques and different wavelengths. The high redshift 4 Gyr providing a lower limit for the accretion time if an LMC motivated asymmetry parameter in the CAS diagram goes from type accretion event happened in NGC 3367. If we consider a strongly perturbed galaxy values and a strong starburst one in lower mass satellites like dark subhalos containing gas, the U and B bands (young stellar component and dust) to the ones time constraint will be definitively shorter (Chakrabarti & Blitz corresponding to a nearly isolated spiral galaxy in the J and K 2010). However, even this scenario does not completely explain bands (average stellar population). why the gaseous component, whose relaxation time is way The azimuthally averaged m = 0,1, and 2 Fourier amplitude shorter than the stellar one, still presents important asymmetries and phases (A , A , A and φ , φ and φ )intheK band (also 0 1 2 1 2 3 both in H-alpha and H i, unless they are currently perturbed. the ones from our deep R-band image for the external regions) The lower panel in Figure 7 shows two solid boxes indicating were estimated finding that the maximum observed variation in clumpiness from B to K 1. up to 1.0 Rd,theA1 distortion is weak (0.05 or lower), bands for a sample of isolated galaxies of Sa–Sb and Sbc–Sm 2. between 1.0 Rd and 2.0 Rd, A1 is slightly higher than the types. NGC 3367 is clearly more clumpy in the optical UBV average for normal galaxies at the same radius, reaching bands than isolated galaxies of similar morphological types. A1 ∼0.15, and This large abundance of SF knots (that are appreciated not only 3. for radii greater than 2.0 Rd, A1 approaches a low limiting along the spiral arms in Figure 1) provides complementary hints value of 0.05. pointing to a past gas accretion scenario. The accretion of cold gas may lower the Toomre local stability We also estimated the Fourier mode amplitude and phase parameter (Q) triggering the clump formation and enhancing a profiles using the Hα intensity map, finding that the amplitude bar (Sellwood & Moore 1999; Block et al. 2002). It might also ranges at least a factor of two higher than in the old stellar produce asymmetrically distributed episodes of SF, producing component in the same radial interval. Finally, as shown in a lopsided structure particularly in the young stellar component Section 6,theHi-integrated line profile and H i surface density and gas (Bournaud et al. 2005). The same mechanism can also distributions are highly asymmetric, indeed more than the explain the starburst phase (Dekel & Birnboim 2006) and the average stellar component. high bar amplitude for the morphological type. A combined The diagnostics discussed above indicate that the A asym- 1 mechanism of external accretion and bar radial transport of gas metry is present across wavelengths and also in the ionized and and stars might be responsible of the color profiles presented in neutral gaseous component, suggesting that lopsidedness is a Section 4.1, and also of the large A amplitude in blue colors property of the potential and not only an artifact of the SF pat- 1 (Mapelli et al. 2008). Although gas accretion seems an attractive tern. Several scenarios have been suggested as possible origin scenario, from the H i VLA observations we find no convincing for lopsidedness, from tidal perturbations triggered by massive evidence for extraplanar gas in the gas kinematics, concluding companions, satellite galaxy accretion, high-speed encounters that the gas asymmetry may be the result of a past event. The (flyby), gas accretion through cosmic filaments, and internal in- gas relaxation time constraints the time of the event to be a stabilities (Rix & Zaritsky 1995;Walkeretal.1996; Bournaud few million years. As a coincidence, if we assume that the et al. 2005;Duryetal.2008). The isolated galaxy instability radio jet speed is one-tenth the speed of light with a projected is an attractive possibility based on NGC 3367 environment, radius of 6.5 kpc, the ejection time is constrained to a similar however, it is not obvious why different mass components show short timescale suggesting that the same accretion event may be different lopsidedness amplitude. Among the external perturber responsible of both morphology and nuclear activity. scenarios, Bournaud et al. (2005) extensively discuss the sur- vival time for the asymmetry triggered inside the disk by a 8.3. Evidence of Secular Evolution in NGC 3367 satellite galaxy accretion. A comparison of our A1 mode analysis with their Figure 12 could be used to constrain the time Bar structural and kinematic properties are correlated with elapsed after a possible minor intruder to be longer than 2 Gyr. its dynamical history. We determined the bar strength using Extra constraints can be set based on the lack of a central two complementary methods, showing that NGC 3367 has a classical bulge, the absence of stellar low SB plumes at the disk strong bar. The B − I color map revealed conspicuous dust lanes edge (at the limit of our observations), and the lack of localized whose shape is sensitive to the bar pattern speed. Specifically, regions with different stellar population (colors). Our finding of the dust lane orientation non-parallel to the bar major axis a pseudo-bulge in NGC 3367 suggests that the stellar and total may suggest a relatively slow bar, which is not unexpected mass of a past perturber was small enough to avoid the formation in late-type galaxies (Salo et al. 1999), however, a definitive of a classical bulge. We use the study presented recently by answer must wait for direct estimation. The bar ellipticity and Villalobos & Helmi (2008) in order to give an interpretation overall structure suggest a spheroid presence absorbing angular to the absence of low SB plumes. This study shows N-body momentum from the bar triggering its growth. Because the simulations aimed at tracking the formation of thick disks at 2D photometry does not indicate an important bulge, the bar different epochs; conveniently they analyze the evolution of structure may indicate the presence of a dark matter component. the host disk and satellite perturber stellar distribution. They However, the lopsided structure and the possible gas accretion

13 The Astronomical Journal, 142:182 (17pp), 2011 December Hernandez-Toledo´ et al. introduce an uncertainty that cannot be sorted out without further et al. 2007;Roskarˇ et al. 2010). The highly inclined jet in investigation of the angular momentum history if m = 2 and m = NGC 3367 (Garc´ıa-Barreto & Rosado 2001) might well be the 1 modes coexist in gas-accreting disk galaxies. Comparison of result of a nuclear inclined disk triggered by misaligned gas images in the K, U, and B bands suggests that secular evolution accretion. The fact that statistical studies show an unexpectedly has triggered gas inflow and SF along the bar. In particular the high fraction (22%) of active isolated galaxies (Sabater et al. U and B morphology suggest a very thin and curved bar and 2010) as well as asymmetric isolated disk galaxies (30%) also a blue compact nucleus suggesting SF along the bar. The (H.M.Hernandez-Toledo´ et al. 2011, in preparation), and NIR torque strength parameter indicates that NGC 3367 has an also that roughly half (44%) of the Seyfert/LINER galaxies outstandingly strong bar, which probably relates to the nuclear in a distance limited sample show radio jet-like structures activity and is consistent with the molecular gas abundance in at kpc scale (Gallimore et al. 2006), suggests that asymmetric the bar region. gas accretion, isolated lopsided, barred galaxies, and nuclear The bulge of NGC 3367 is exponential, similar to the so-called activity may be correlated. If this is confirmed by the future pseudobulges. Bulges of this type are thought to be generated corresponding statistical multiwavelength studies, large-scale via internal secular evolution processes (see, e.g., Kormendy & gas accretion may rise as an important source of nuclear galaxy Kennicutt 2004). Given that NGC 3367 is isolated, secular evo- activity. Furthermore, we can expect that at high redshift, when lution is likely the dominant evolutionary mechanism. Pseudob- filament accretion rate was more vigorous and common (gas ulges typically resemble small disks embedded in larger ones and satellites), the AGN feedback triggered only by the cold or flattened spheroids. The strong bar presence and the large accretion mode and enhanced by disk asymmetries may be abundance of young stellar clumps in the disk (Garc´ıa-Barreto considerably more important than typically assumed. et al. 2007; Elmegreen et al. 2008) support this scenario as a NGC 3367 can be added to the list of local late-type galaxies possible one for NGC 3367 bulge formation. Foyle et al. (2010) that lack a classical bulge but that host an obscured AGN observationally estimated the effect of gravitational torques due (McAlpine et al. 2011; Ghosh et al. 2008; Desroches & Ho to the present day global disk stellar distribution. They discussed 2009). This type of galaxy may reveal kiloparsec-scale jet- whether these torques are efficient at transporting angular mo- like structures in deep enough radio imaging of local surveys. mentum within a Hubble time. They found that torques due The black hole mass in this pseudo-bulge galaxy has been to the stellar disk lead on average to outward angular momen- recently estimated using various methods, ranging between 5 7 tum transport over much of the disk (r 3 rexp). Gravitational 10 and 10 M (McAlpine et al. 2011). torques induce angular momentum change on timescales shorter than a Hubble time inside one scale length, where they act on 8.5. Constraining Formation Scenarios a timescales of 4 Gyr. If we compare our results with those of with Foyle et al. (2010), secular evolution is thus expected to The discussion presented above favors the following facts. be effective in the inner parts of NGC 3367 and perhaps is also 1. NGC 3367 is a galaxy likely localized in a low-density connected with the nuclear activity, however, the details for this environment. The nearest dense structure is the Leo Group, process and its relationship to the fueling of the central AGN in however, the difference in line of sight velocity is near NGC 3367 need to be worked out. to 2000 km s−1, considerably larger than Leo’s escape velocity, therefore, we think they are unlikely bounded. 8.4. Nuclear Activity and NGC 3367 Structure 2. The importance of major mergers in NGC 3367 assembling NGC 3367 is a Seyfert2/liner galaxy presenting a radio con- and even of minor mergers with massive satellites is tinuum jet, however, it is still considered a radio quiet galaxy. severely constrained because of the lack of a classical A natural question is what is the connection, if any, between bulge as well as the absence of bright and thin stellar the nuclear activity and the asymmetric galaxy morphology? As streams. In fact the B/D ratio 0.07–0.11 marginally favors we concluded above, the most compelling candidate scenario a pseudobulge, perhaps caught in the act of formation. This for being responsible for NGC 3367 morphology is a past gas galaxy is an example of the late-type active ones discussed rich accretion event. Currently cosmological galaxy formation by Schawinski et al. (2011). The possibility of a gas rich scenarios provide an explanation of both possibilities; galaxies minor merger although not discarded is constrained to 12 smaller than 10 M receive significant accretion (small galax- current very low mass satellites or toward the past 3–4 Gyr. ies and gas) through cosmic filaments (Dekel et al. 2009). The For comparison, typical fractional lopsidedness amplitude main argument favoring this scenario is the lack of dynamically A1 within the central 5 kpc from Two Micron All Sky young stellar signatures associated with a recent tidal event. Survey (2MASS) images of advanced mergers of galaxies Specifically the absence of thin tidal tails constrains any inter- (Jog & Maybhate 2006)gofrom∼0.12 to 0.2, higher action event to some dynamical times in the past (3–5 Gyr; see than the values found in the inner regions of NGC 3367. cf. Villalobos & Helmi 2008), however, the gas component that Note that those advanced mergers were selected as having has a shorter relaxation time shows both a global (A1 mode) merged into a single nucleus but still show indications of and localized overdensities. That short gas relaxation time com- interactions, including visible tidal tails, contrary to what pared with the stellar component suggests a perturbing event is observed in NGC 3367. in the last hundreds of million years. The images in short (U 3. The stronger asymmetry found in the young stellar compo- and B) wavelengths reveal young stellar population all the way nent and gas constrains a possible perturbation on the gas along the bar up to the nucleus suggesting that a continuous gas relaxation timescales which are shorter than the stellar re- supply has been channeled by the bar toward the nuclei. laxation times (a Gyr), therefore the gas perturbation must Cosmological simulations of galaxy formation show that have happened a few million years in the past. accreted gas (either from satellites or cold flows) frequently 4. The high clumpiness parameter value and the global star- has a different angular momentum orientation compared with burst phase (see Figure 7) may be explained if the gas the existing disks originating warps or polar disks (Maccio` richness is high. Based on the integrated H i line profile and

14 The Astronomical Journal, 142:182 (17pp), 2011 December Hernandez-Toledo´ et al.

Table 2 Morphological Properties of NGC 3367 from This Work and Other Properties

Morphology R’SBcd(r) Circumnuclear disk or ring Incl 25◦ ± 5◦ at 80 arcsec Bulge Sersic´ n = 1–1.8 Bar Length 17 arcsec (7 kpc) P.A. 66◦ ± 4 = ± max = = max 0.58 0.05 QT (R) 0.44 (hz 325 pc) Lopsidedness CAS UBV starburst CAS R weakly interacting CAS JK isolated galaxy Fourier NIR ∼0.05 r < 1.0 Rd (0.12,0.11,0.11) (J,H,K)1.5Rd < r < 2.5 Rd ∼0.05 r > 2.5 Rd Fourier Hα>2 at all radii w.r.t. NIR Fourier H i (VLA) A = 2.2 > w.r.t. NIR Other relevant data − o (B V )T 0.47 Garc´ıa-Barreto et al. (2007) 9 MH i (10 M) 7 Huchtmeier & Seiradakis (1985) 9 MH2 (10 M) > 3Garc´ıa-Barreto et al. (2005) Log (LB) 10.68 Tully (1988) 10 Log (LFIR)(10 L) 10.33 − SFR (M yr 1)3–4

CO observations, NGC 3367 has a gaseous mass of a few mark on the importance of clump migration as a black 10 10 M (Huchtmeier & Richter 1989;Garc´ıa-Barreto et al. hole feeding mechanism. 2005). A naive estimation of the stellar mass is severely affected by the AGN light and by dust extinction. For example, if we use published K-band photometry, a maximum 9. CONCLUSIONS rotation velocity close to 300 km s−1 or larger is inferred from the Tully–Fischer relation. In contrast, Garc´ıa-Barreto From a set of optical, NIR, and Hα Fabry–Perot observations & Rosado (2001) present estimates of the galaxy maximum − carried out at San Pedro Martir,´ National Optical Observatory rotation velocity in the range of (195–225) km s 1, not far in Mexico,´ and from archive H i VLA data we study some from the reported values for the Milky Way. As a compari- structural properties in NGC 3367 and tried to constrain possible 10 son, the Milky Way has a stellar mass around 6 ×10 M origins for its asymmetric structure. and a gas-to-baryon fraction of 13%. Avoiding a detailed Our surface photometry analysis and coupled 1D–2D bulge/ modeling of the disk and nuclear emission required to es- bar/disk decomposition procedures indicate that both the bulge timate the stellar mass, and using recent theoretical stud- and disk of NGC 3367 are consistent with a double exponential ies (Baldry et al. 2008; Rodr´ıguez-Puebla et al. 2011) that luminosity distribution in all the observed wavelengths with suggest a relationship between the total galaxy mass and a rather small B/D luminosity ratio suggesting an R’SBcd(r) = −1 the stellar mass, we can assume a Vmax 225 km s morphological type with a pseudobulge constraining the mass for NGC 3367 and infer a stellar mass of the order of of a possible past perturber to rather low values. From the 10 6 ×10 M. Since the gas mass can be directly estimated position of the galaxy in the CAS structural diagrams, it is from the observations, the inferred gas-to-baryon fraction inferred that NGC 3367 is in a global starburst phase, with an −1 attains 16%. On the other hand, if we assume a lower limit SFR ∼ 3–4 M yr . of Vmax, we can infer a gas fraction of about (25–30)%. A qualitative comparison of the observed dust lane morphol- The estimated gas richness in NGC 3367 (16%–30%) ogy from (B − I) color index maps with the results from bar when compared to galaxies of similar Vmax like the Milky numerical simulations suggests that NGC 3367 may host a rel- Way (13%) suggests that the gaseous disk has been ex- atively slow bar. Bar torques, estimated from the NIR images periencing fragmentation and localized stellar bursts (see (Buta & Block 2001), yielded a bar strength Qb = 0.44, placing Figure 7 and Garc´ıa-Barreto et al. 2007). NGC 3367 as a galaxy with a very strong bar. The presence of 5. The scenario resembles truly rich gas galaxies at z>1, such a bar may be behind the complete absence of H i gas in where disk fragmentation is believed to contribute to the central regions of NGC 3367, mostly covered with a high bulge formation (e.g., Ceverino et al. 2010). However, amount of CO gas instead. The absence of such bars may ex- note that NGC 3367 is less gaseous and less violently plain why other similarly asymmetric galaxies like M101 do not unstable. If this analogy is correct, disk clumps infall due currently present strong nuclear activity. to dynamical friction may be forming now a pseudobulge Global and local asymmetry in NGC 3367 has been analyzed (Elmegreen et al. 2008) and may be feeding the central black from three alternative indicators: (1) through the CAS structural hole growth and activity. Recent observational evidence parameters in the optical and NIR light, (2) from an estimate (Kormendy et al. 2011) found no correlation between of the Fourier amplitude of the m-components of the density pseudobulge and black hole masses, setting a question distributions in the NIR and Hα light, and ﬁnally (3) from a new

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